For several decades it has been a goal of industry to make plastic sheet materials either biodegradable by microorganisms or environmentally degradable by sunlight, moisture, temperature and the like. Usually after environmental degradation, plastic sheet materials are then more susceptible to assimilation by microorganisms. In spite of considerable efforts, our lands are becoming inundated with plastic sheet materials, and articles made therefrom, that will not degrade perhaps for centuries. It is therefore a continuing goal to make plastic sheet materials as fully degradable or compostable as possible. A compostable material is one that under-goes chemical, physical, thermal and/or biological degradation such that it may be incorporated into and is physically indistinguishable from finished compost (humus) and which ultimately mineralizes (biodegrades to CO.sub.2, water and biomass) in the environment like other known compostable matter such as paper and yard waste. It would be highly desirable to provide a plastic sheet material that is compostable especially in a municipal solid waste composting facility where it may undergo biodegradation in the presence of heat, moisture and microorganisms.
There is a particular need for compostable plastic sheet material in disposable diapers, underpads, hygienic pads and the like. These products for practical purposes must satisfy such properties as water impermeability in order to prevent seepage of urine and other human waste products therethrough. In addition, such sheet materials must have sufficient tear, tensile and impact strengths to function in such useful articles. These same properties that make them useful, however, lead to their lack of biodegradability. A few examples of patents directed to biodegradable and environmentally degradable polymer compositions or products include U.S. Pat. Nos. 3,901,838; 3,921,333; 4,016,117; 4,021,388; 4,120,576; 4,125,495; 4,218,350 and 4,420,576.